This invention relates to the continuous casting of metals in strip form between a pair of moving surfaces constituted by endless flexible heat-conducting bands or belts, as in a so-called twin-belt caster wherein the belts are trained over pulleys or the like. More particularly, the invention is directed to improvements in belt pulley devices, and belt-steering methods employing such pulleys, in twin-belt continuous casting apparatus and procedures.
In exemplary belt-casting apparatus of the type herein contemplated, a pair of endless metal belts are caused to travel in substantially parallel paths so as to define a mold space between them, closed at its sides by suitable edge dams. The molten metal is supplied to one end of the space and discharged from between the moving belts at the exit end, as a fully solidified strip of predetermined thickness in the range from the thickness of slab to relatively thin plate or sheet. Arrangements have been provided for cooling the reverse faces of the belts, to remove heat as necessary for solidifying the metal.
It is of great importance, in such apparatus, to maintain exact positional stability of each belt in a precise, desired path. Typically, the belts are trained over drive pulleys, i.e. suitably driven rotary members for imparting continuous unidirectional motion to the belts, as well as over guide pulleys or rollers or other bearings cooperatively defining the path of belt movement. As casting operation proceeds, the belts (which are in the nature of relatively wide metallic webs) commonly tend to undergo lateral displacement with respect to the pulleys, owing to such factors as transverse taper or other departure from flatness of the belts, differential thermal strains on the belts, and/or variations in pulley diameter from side to side of the pulleys. This lateral wandering of the belts may indeed be progressive in character, so that the belts exhibit increasingly severe positional deviation over the course of a number of revolutions. It is accordingly necessary to provide corrective measures in order to maintain proper positional alignment of the belts with the centerline of the casting apparatus.
Expedients heretofore employed or proposed for this purpose have included arrangements for elastically affecting the belt length differential (from side to side) and/or moving the belt-pulley system sideways to keep the belt aligned with the casting apparatus centerline. These expedients are, however, structurally and operationally complex and in many cases inconvenient.